Polyvinyl chloride (PVC) is widely used in both its rigid and flexible forms in such applications as films, siding, sheets, pipe and tubing. Because rigid PVC is a hard, brittle thermoplastic polymer, it is often mixed with a modifier to form a composition that is less prone to failure on impact. For example, in U.S. Pat. Nos. 3,006,889 and 3,209,055 the use of a broad range of chlorinated and chlorosulfonated polyethylenes in blends with PVC is disclosed. In addition, various types of specialty chlorinated polyethylenes have been used as impact modifiers. For example, chlorinated polyethylenes having low blocking tendencies that are prepared from polyolefins having melt indexes (I2) of 0.3 dg/minute and 0.2 dg/minute are disclosed as impact modifiers for PVC in U.S. Pat. No. 4,767,823. Further, impact modifiers that are mixtures of chlorinated polyethylenes with other polymers have been disclosed. As an example, Aono et al., in Japanese Unexamined Patent Application Hei 7-11085, disclose the use of a mixture of a chlorinated polyethylene prepared from a polyethylene of molecular weight 50,000 to 400,000 and AES resin (acrylonitrile-EPDM-styrene), optionally in combination with other polymers, as an impact modifier for PVC.
Despite the extensive prior art that exists related to chlorinated polyethylene impact modification of PVC, economical compositions that exhibit exceptionally good impact strengths in the ambient to low temperature range have not been disclosed. Such compositions would be useful in applications such as siding, profiles and pipe.
Impact strength is not the only physical property of PVC that can be improved by addition of chlorinated polymeric additives. For example, in U.S. Pat. No. 4,481,133 a method for improving extrudability of PVC/chlorinated polyethylene blends is disclosed that involves mixing PVC with chlorinated polyethylene of molecular weight 10,000 to 12,000,000 (preferably 60,000 to 500,000), and a fluoropolymer. The benefits of blending PVC with more than one type of chlorinated polyethylene are disclosed by Klug, et al. in U.S. Pat. No. 4,280,940. The Klug reference discloses an easily processed blend of PVC and two chlorinated polyethylenes, where the first chlorinated polyethylene is prepared from polyethylene having a melt flow index 190/5 (i.e. I5 at 190° C.) of preferably 0.3-3.5 g/10 minutes (0.3-3.5 dg/minute) and the second chlorinated polyethylene is prepared from polyethylene having a melt flow index 190/5 preferably of from 40-55 g/10 minutes (40-55 dg/minute).
With regard to PVC compositions useful in the ambient to low temperature range, it would be desirable to have a composition that is characterized by excellent impact resistance in combination with ease of preparation. Efficient manufacture of PVC/additive compositions requires that the blends exhibit an appropriately low fusion temperature and fusion time. Fusion temperature refers to the temperature at which a mixture of PVC and an additive form a homogeneous system. In order to incorporate an additive into PVC, it is necessary to heat the PVC while blending in the additive. Short fusion times and low temperatures are desirable because PVC is susceptible to decomposition at melt temperatures. An impact modifier that has a low fusion temperature and short fusion time would consequently have definite processing advantages in manufacture of PVC compositions.